The present invention relates to a system for conducting the identification and quantification of micro-organisms, e.g., bacteria, in biological samples such as urine. More particularly, the invention relates to a system comprising a disposable cartridge and an optics cup or cuvette having a tapered surface. The system may utilize the disposable cartridge in a sample processor and the optics cup or cuvette in an optical analyzer, wherein the optics cup also has a floor in the shape of an inverted arch.